Easily flowable, impact resistant polyamides

ABSTRACT

Easily flowable, impact resistant polyamide moulding composition containing from 0.5 to 10%, by weight, of polyethers preferably modified with (meth)acrylate or primary amino end groups or of polyesters preferably containing (meth)acrylate end groups.

This is a continuation of copending application Ser. No. 701,146 filedFeb. 13, 1985, now abandoned, which in turn was a continuation ofapplication Ser. No. 447,972 filed Dec. 8, 1982, now abandoned.

This invention relates to highly fluid, impact-resistant polyamidemoulding compounds containing from 0.5 to 10%, by weight, of end groupmodified polyethers or polyesters having molecular weights of from 500to 10,000 and softening points below 100° C.

The impact strength of moulded products of polyamides depends to a largeextent on the water content of the moulded products. In the anhydrousstate, e.g. after production of the moulded products by injectionmoulding, those moulded products which have been produced from highlyfluid and therefore easily processable polyamides of medium molecularweight, and among these especially those obtained from highlycrystalline polyamides, are relatively sensitive to impact stresses.

Although moulded articles of relatively high molecular weight polyamidessuch as those preferably used for extrusion processing are lesssensitive to impact, they are more difficult processed because of thesubstantially higher melt viscosity and the consequently lower fluidityof the polyamides used.

Moreover, the preparation of more highly viscous polyamides frequentlyrequires a costly and elaborate solid phase-after-condensation step.

There is therefore a need for highly fluid polyamide moulding compoundswhich may be processed easily and from which moulded products havingincreased impact strength in the dry state can be produced. Ofparticular interest are those polyamides in which high tensile strengthand ease of processing are combined with high impact strength.

Various methods for increasing the toughness of polyamides are known.These include, for example, the incorporation of low molecular weightplasticizers in the polyamides. This method fails to provide asatisfactory solution to the problem for various reasons. Most of theplasticizers which are suitable for synthetic materials are notsufficiently compatible with polyamides and migrate from the compositionin the course of processing respectively tend to bleed out. On the otherhand plasticizers which are compatible and form real solutions withpolyamides in most cases impair the good mechanical properties of thepolyamides. Highly polar, low molecular weight substances, such as wateror dimethyl formamide do provide some improvement in the toughness ofthe polyamides, but they can be only incorporated into the polyamidemoulded products after they have been formed because these additiveshave relatively low boiling points and thus would cause blisters in thearticles.

This method is therefore generally too time-consuming and costly andunusable for the production of thick-walled moulded articles owing tothe uneven distribution of the additives.

According to other methods the impact strength of polyamides is improvedby the addition of certain polymeric substances. Thus, polyethylenes andcopolymers of vinyl acetate and ethylene have been used with moderatesuccess.

Better results have been obtained, for example, with olefinic copolymerscontaining COOH groups and with corresponding graft polymers.

This also applies to the modification with rubber polymers, e.g. withgrafted acrylonitrile or polybutadiene rubber particles or withelastomeric blocks incorporated into the polamide by polycondensation.The toughness achieved, however, is not sufficient for certainapplications.

Numerous attempts to prepare relatively high molecular weight polyamideswithout a solid phase after-condensation have been carried out with theaim of achieving chainbranching or cross-linking.

Polyfunctional epoxides, for example, and especially polyfunctionalisocyanates are in principle suitable for this purpose.

These methods may indeed result in products having increased toughnessbut since the melt viscosity of the polyamide is usually also greatlyincreased processing by injection moulding may become very difficult.

It has now surprisingly been found that impact resistant, highly fluidpolyamide moulding compounds which do not have the disadvantagesmentioned above are obtained when polyamides are mixed with certain endgroup-modified polyethers and/or polyesters which have softening pointsbelow 100° C. The moulded products obtained from these compounds havesubstantially improved toughness which is comparable with that ofpolyamides having a considerably higher molecular weight.

It is surprising that the fluidity of the polyamide is not reduced bythe modification, but remains substantially the same or is in many casesconsiderably improved. The fluidity may be adjusted by the type ofmodifier and by suitable choice of the flow length of the polyamide. Themodification leaves the modulus of bending substantially unchanged.

The present invention therefore relates to easily flowablethermoplastically processible polyamide moulding compositions whichcontain from 0.5 to 10%, by weight, preferably from 2 to 6%, by weight,based on the polyamide,of at least one end group-modified polyetherand/or polyester having a molecular weight of from 500 to 10⁴,preferably from 10³ to 5×10³ and a softening point below 100° C.

Suitable end groups for the polyethers and polyesters are: residues ofα,β-unsaturated monocarboxylic acids, carbonic and oxalic acid esters,epoxides, primary and/or secondary amines, N-α-hydroxymethyl lactams andsimilar compounds in which the polyether or polyester basis is notdirectly attached to the above-mentioned end groups, but, for example,by way of a polyurethane group.

The modifiers used are preferably polyesters and polyetherscorresponding to the following general formula:

    R--(X).sub.n

wherein

R represents a n-valent (poly)ether and/or (poly)ester group having anaverage molecular weight of from 500 to 10,000, preferably from 1000 to5000; and

n represents an integer from 1 to 4, preferably 2; when R represents apolyether radical, X represents one of the following groups X₁ to X₈ ;

X₁ represents --O--CO--CR¹ ═CH₂ wherein R¹ represents H or CH₃ ;

X₂ represents --NR² H wherein R² represents H or C₁₋₁₈ alkyl;

X₃ represents --O--CO--O--R³ wherein R³ represents C₁₋₁₈ alkyl oroptionally substituted aryl having from 6 to 19 carbon atoms;

X₄ represents --O--CO--CO--O--R³ ; wherein R³ is as defined above; X₅represents ##STR1## wherein m presents an integer of from 4 to 11;

X₆ represents ##STR2## wherein A represents a bond or ##STR3## wherein

Z represents a (cyclo)aliphatic group having up to 10 carbon atoms, anaromatic C₆₋₁₆ group or an aliphatic aromatic C₇₋₁₈ group;

and the epoxide groups have optionally been reacted with (meth)acrylicacid or with hydroxyalkyl (C₁ --C₅) (meth)acrylate;

X₇ represents ##STR4## and

X₈ represents ##STR5## wherein

Q represents a polyurethane group.

The groups O--CO--CR¹ ═CH₂ and --NR² H are preferred. When R representsa polyester residue suitable end groups are

X₁, X₃, X₄, X₆, preferably X₁ and X₆.

Methods of preparing the modifiers are known from the literature.

Modified polyethers are preferred, inter alia on account of the easewith which they may be dosed (viscosity) and the ease of preparationthereof.

It is particularly preferred to use polyethers having (meth)acrylate orprimary amino end groups.

The molecular weights of the polyether and polyester groups indicatedare determined from the OH number or amine number of the startingcomponents. It is also possible to determine the molecular weight(M_(n)) by vapour-depression-or membrane-osmose-methods.

The polyamides used for the purposes of the present invention may belinear polycondensates of lactams or corresponding amino acids havingfrom 4 to 12 carbon atoms or conventional polycondensates of diaminesand dicarboxylic acids, such as 6,6-, 6,7-, 6,8-, 6,9-, 6,10-, 6,12-,8,8- or 12,12-polyamide or polycondensates of aromatic dicarboxylicacids, such as isophthalic acid or terephthalic acid, with diamines,such as hexamethylene diamine or octamethylene diamine, orpolycondensates of araliphatic starting materials, such as m- orp-xylylene diamines, and alipic acid, suberic acid or sebacic acid, andpolycondensates based on alicyclic starting materials, such ascyclohexane dicarboxylic acid, cyclohexane diacetic acid,diamino-dicyclohexyl methanes or isophorone diamine.

Mixtures of the above-mentioned polyamides or copolyamides which may beobtained from the above-mentioned components may also be used. Thesoftening points of the polyamides used as starting materials should beat least 150° C. Partially crystalline polyamides are preferably used.

The relative viscosity of the polyamides to be used should generally beat least 1.8 (determined in a 1% solution in m-cresol at 25° C.).

It is particularly preferred to use the 6,-, 6,6-, 6,9-, 6,10-, 6,12-,11- and 12-polyamides conventionally used for the production ofinjection moulded articles, as well as copolyamides which aresynthesized predominantly like the above-mentioned polyamides and haverelative viscosities of from 1.8 to 5.0, preferably from 2.0 to 3.5measured as indicated above.

Instead of polyamides, there may be used polymer blends which consistpredominantely of polyamides, preferably to an extent of at least 70%,by weight, and further polymeric components which may consist mainly ofknown elastic polymers, such as a polyolefin or olefinic copolymer,preferably a copolymer containing polar groups, as well as correspondinggraft (co)polymers.

Products of this type are known and have been disclosed, e.g. in GermanAuslegeschrift No. 1,241,606 and German Offenlegungsschrift No.2,758,568.

To prepare the modified polyamides according to the present invention,the polyamide component and the modifier may be mixed together at atemperature above the melting point of the polyamide. This may becarried out, for example, immediately after preparation of thepolyamide, by mixing the modifier with the melt which is to be spun intoa strand. The modified polyamides according to the present invention arepreferably prepared by mixing the starting components in conventionalmixing screws.

This method would be chosen particularly if, in addition to thepolyamides, other polymers are to be incorporated for the preparation ofmodified polymer mixtures, or other additives, such as stabilizers,mould release agents, lubricants, crystallisation accelerators,plasticizers, pigments, dyes, reinforcing agents and/or fillers, such asglass fibres or asbestos, are to be incorporated.

For compounding the components, each conventional well known apparatusmay be employed. Double screw extruders are preferred.

The polyamides which have been modified according to the presentinvention are easily flowable and can be therefore easily be processedinto moulded articles in the conventional injection moulding machines.These moulded articles are distinguished by the improved notched impactstrength as well as having the other advantageous properties typical ofpolyamides.

Moulded articles obtained from the polyamide moulding compositionsaccording to the present invention may be more easily removed from themould than unmodified products even if they do not contain specialadditives for this purpose, and they are also distinguished by very goodsurface characteristics.

I. PREPARATION OF THE MODIFIERS EXAMPLE A

5.6 g of acrylic acid,

2100 g of an ethylene oxide/propylene oxide copolyether tipped withethylene oxide (OH number 28, bifunctional, iodine number 0 to 1,molecular weight M_(n) about 4000),

18.5 g of p-toluene sulphonic acid dissolved in 18.5 g of water,

3.26 g of 2,5-di-t-butyl-hydroquinone,

2.16 g of p-methoxy-phenyl,

2.16 g of 2,6-di-t-butyl-4-methyl-phenol, about 900 g of toluene

are boiled on a water separator at from 125° to 130° C. while air isslowly introduced. Toluene is distilled off when acid number 4 has beenreached. The product is an almost colourless, low viscosity liquid ofacid number 6.

EXAMPLES B-G

The following (meth)acrylate polyethers respectively polyesters (E) areprepared in a manner analogous to Example A:

B: Bis-acrylate of a polyethylene glycol having molecular weight of 200

C: Monoacrylate of a monofunctional propylene oxide/ethylene oxidecopolyether (molecular weight 2800)

D: Bis-acrylate of polytetrahydrofuran (molecular weight 2000)

E: Bis-acrylate of a polyester diol having molecular weight 2000obtained from dimeric fatty acid (Empol 1010®)/hexane diol

F: Bis-acrylate of a polyether of tetrahydrofuran and decene oxide(molecular weight 1750)

G: Bis-methacrylate of a propylene oxide/ethylene oxide copolyether,ethylene oxide-tipped (molecular weight 2000).

The molecular weights were calculated from the OH numbers of the mono-or poly-ols.

The products obtained from Experiments B to G are almost colourless toyellowish and the acid numbers are in the range of from 2 to 6. Theproducts are easily dosable liquids having low viscosities with theexception of Example D, which is a solid product giving a highly fluidmelt at above the temperature of about 37° C.

EXAMPLE H

1 kg of a bifunctional polyether diol based on propylene oxide andhaving a molecular weight of 2000, 1 kg of diethyl carbonate and 3 g ofsodium methylate were heated to boiling with stirring. Ethanol was drawnoff from the top of the column in the course of 20 hours and thediethyl-carbonate excess was subsequently removed under vacuum.

The residue was a low viscosity, pale liquid.

EXAMPLE K

1 kg of the polyether diol used in Example H is heated to boiling understirring with 1 kg of diethyl oxalate and 3 g of sodium methylate.

Ethanol was drawn off at the top of the column in the course of 20 hoursand the diethyl oxalate excess was subsequently removed under vacuum.The residue is a low viscosity, pale liquid.

EXAMPLE L

1 kg (0.5 mol) of a polyether (as used in Example G) was reacted with148 g (1 mol) of phthalic acid anhydride for 5 hours. The product (acidnumber 60) together with 5.7 g of p-toluene sulphonic acid was slowlyadded dropwise to 380 g (1 mol) of bisphenol A-bis-glycidyl ether at100° C. The end product had a residual acid number of 3.8 and is amedium viscosity liquid.

EXAMPLE M

1 kg (0.5 mol) of a polyether (as used in Example G), 158 g (1 mol) ofN-methoxy-methyl caprolactam and 1 g of p-toluene sulphonic acid weretogether heated to 122° C. for 5 hours, 137° C. for 3 hours and 156° C.for 3 hours. Methanol was split off in the process. The residue is abrown liquid having a nitrogen content of 1.2%, by weight.

EXAMPLE N

1 kg (0.5 mol) of a polyether (as used in Example G) and 218 g (1 mol)of pyromellitic acid anhydride were heated to 120° C. within 1.5 hoursand then stirred at 120° C. for one hour.

A medium viscosity liquid having an anhydride acid number of 41 and afree acid number of 96 was obtained.

II. PREPARATION OF THE MODIFIED POLYAMIDES EXAMPLE 1

97 parts, by weight, of a 6-polyamide having a relative viscosity of 2.8determined in a 1% solution in m-cresol at 25° C., a notched impactstrength according to DIN 53453 of 2.37 kJ/m² and a flow length.sup.(*)of 65 cm and 3 parts by weight of the acrylate polyether of Example Aare added separately into a double screw extruder (Model ZSK 53) usingdosing balances or a dosing pump and extruded at 90 revs per min. and260° C. The homogeneous melt is spun as a strand into a bath of water,granulated and dried at from 80 to 100° C. to a water content of lessthen 0.1%, by weight. The product has a relative viscosity of 2.73, anotched impact strength of 4.3 kJ/m² and a flow length of 74.5 cm. Theflexural stress is 111 N/mm² (DIN 53 452).

EXAMPLE 2

Polyamide-6 is modified with 10%, by weight, of the acrylate polyetherof Example A as described in Example 1. The results of measurements areentered in Table 1.

COMPARISON EXPERIMENT 1

The relative viscosity and the notched impact strength of a polyamide-6are increased by conventional after-condensation, which is accompaniedby a loss in flowability. The relevant properties are entered in Table1.

COMPARISON EXPERIMENT 2

Polyamide-6 is prepared in an autoclave by conventionalpolycondensation, using acetic acid as chain-terminating agent. Thepolymer is easily flowable, but is not sufficiently tough for practicalpurposes, see Table 1.

EXAMPLE 3

Polyamide-6 having a rel. viscosity of 2,1 is extruded together with 6%of the acrylate polyether of Example A by the method described inExample 1. The results are summarized in Table 1.

EXAMPLES 4-6

The experimental procedure described in Example 1 is repeated, but thepolyamide is also varied. The composition of the products and theproperties thereof are summarized in Table 1. Polyamide-6,6 is extrudedat 275° C.

                                      TABLE 1    __________________________________________________________________________                                  Modifier Modified polyamide           Polyamide                   Parts,      Flow                 Parts, by                      a.sub.k                           Flow length by     a.sub.k                                                   length           Type              η.sub.rel                 weight                      (KJ/m.sup.2)                           (cm)   Example                                       weight                                           η.sub.rel                                              (KJ/m.sup.2)                                                   (cm)    __________________________________________________________________________    Example    1      6-PA              2.8                 97   2.37 65     A    3    2.73                                              4.3  75    2      6-PA              2.8                 90   2.37 65     A    10  2.9                                              10.3 67    3      6-PA              2.1                 94   0.9  100    A    6   2.0                                              5.2  100    4      6,I-              2.4                 97   2    27     A    3   2.5                                              6.0  28           PA    5      6,6-              2.9                 97   2.1  75     A    3   2.9                                              5.4  93           PA    6      6,6-              2.9                 94   2.1  75     A    6   2.8                                              6    95           PA    Comparison    example    1      6-PA              2.8                 100  2.37 65     --   0   3.8                                              4.5  30    2      6-PA              2.1                 100  0.9  100    --   0   -- --   --    __________________________________________________________________________     a.sub.k =  notched impact strength according to DIN 53453 in the freshly     injected state     6PA = polycaprolactam     6,IPA = polyhexamethylene isophthalamide     6,6PA = polyhexamethylene adipamide

EXAMPLES 7-12

Polyamide-6 having a relative viscosity of 2.8 is extruded with various(meth)acrylate polyethers respectively polyesters according to theprocedure described in Example 1. The properties of the modifiedpolyamides determined are summarized in Table 2.

COMPARISON EXPERIMENT 3

Polyamide-6 is extruded as described in Example 1 with the modifier ofExample B which has a low molecular weight of 200. The results are setforth in Table 2.

EXAMPLE 13

67 parts, by weight, of the polyamide from Example 1, 30 parts, byweight, of commercial glass fibres and 3 parts, by weight, of themodifier of Example A are compounded as described in Example 1.

Properties of product:

Relative viscosity: 2.8

Flow length: 62 cm

Notched impact strength: 13.0 kJ/cm²

COMPARISON EXPERIMENT 4

This is a repetition of Example 13 without the use of the modifier ofExample A.

Properties of product:

Relative viscosity: 2.8

Flow length: 43 cm

Notched impact strength: 13.0 kJ/m²

COMPARISON EXPERIMENT 5

The polyamide from Example 1 is treated with an isocyanate to increasethe notched impact strength. The flow length of the polyamide is therebyshortened due to the increase in molecular weight. The results aresummarized in Table 3.

                  TABLE 2    ______________________________________           Modifier        Modified polyamide           Parts, by                  Example         a.sub.k                                         Flow           weight type     η.sub.rel                                  (kJ/m.sup.2)                                         length (cm)    ______________________________________    Comparison             3        B        2.8  2.3    63    experiment 3    Example 7             3        C        2.7  5.4    78    Example 8             9        C        2.7  6.0    84    Example 9             3        D        2.6  7.9    74    Example 10             3        E        2.7  3.6    75    Example 11             3        F        2.7  6.4    82    Example 12             3        G        2.8  4.5    75    ______________________________________

                  TABLE 3    ______________________________________           Modifier      Modifier polyamide    Comparison             Parts, by             a.sub.k                                          Flow length    Experiment             weight   Type   η.sub.rel                                   (kJ/m.sup.2)                                          (cm)    ______________________________________    5        1        H      4.4   3.9    27    ______________________________________     H = Desmodur VK ® (diphenylmethane diisocyanate containing about 35%     of polyfunctional multinuclear components)

EXAMPLE 14

97 parts, by weight, of the polyamide-6 described in Example 1 arecompounded with 3 parts, by weight, of a polyether urethane acrylate ofExample 7 of German Auslegeschrift No. 2,115,373.

Relative viscosity: 2.8

Flow length: 66 cm

Notched impact strength: 4.9 kJ/m²

EXAMPLES 15 TO 20

Polyamide 6 is compounded as described in Example 1 with modifierscontaining various end groups. Modifier P produces such a markedimprovement in the flowability that the flow length amounts to 100 cm.Modification according to Examples H, K, L, M and N produce increases inflow length varying from slight to considerable. The results are shownin Table 4.

COMPARISON EXPERIMENT 6

Polyamide-6 is compounded, as described in Example 1, with the polyetherdiol used in Example H. A very slight improvement in the impact strengthis accompanied by a considerable decrease in rigidity.

                  TABLE 4    ______________________________________           Modifier     Modified polyamide product           Type,            Notched           according        impact           to               Strength Flexural stress           Example % by wt. kJ/m.sup.2                                     N/mm.sup.2    ______________________________________    Example    15       H         3        7.3    112    16       K         3        7.3    115    17       L         3        5.2    115    18       M         3        7.5    110    19       N         3        6.3    110    20       P         6        5.1    --    Comparison    experiment    6        Q         3        3.4     95    ______________________________________     Q = polyether diol as used for Example H     P = bis(3-aminopropyl)-polytetrahydrofuran (Molecular weight 750)

COMPARISON EXPERIMENTS 7-10

For comparison with the products according to the present invention,polyethers having amino end groups were used together with astoichiometric quantity of adipic acid as momonomers for the usualhydrolytic polycondensation of caprolactam. The products showed noimprovement in the impact strength. Only products according tocomparison experiment 10 showed a high notched impact strength, but theflowability and flexural strength thereof were insufficient. Theproducts and the properties thereof are summarized in Table 5.

                  TABLE 5    ______________________________________                  Properties of the Product           Polyether         Notched            used    Flexural impact        Flow    Comparison      % by    strength                                   strength    length    Experiment             Type   wt.     (N/mm.sup.2)                                   (kJ/m.sup.2)                                          η.sub.rel                                               (cm)    ______________________________________    7        I      3       117    2.2    3.1  55    8        II     3       110    2.3    2.8  57    9        II     6       108    2.1    2.8  46    10       II     10       88    8.3    3.1  24    ______________________________________     I = polytetrahydrofuran having 3aminopropyl end groups, molecular weight     1100     II = polypropylene oxidepolyether with OH end groups replaced by     NH.sub.2', molecular weight = 2000

We claim:
 1. Highly fluid, thermoplastically processable poly-amidemoulding composition which comprises a mixture containing a polyamideand a polyamide modifier, said mixture being prepared by mixing thepolyamide component and the modifier component at a temperature abovethe melting point of the polyamide in mixing screws, wherein themodifier component is from 0.5 to 10%, by weight, of at least one endgroup modified polyether and/or polyester having a molecular weight offrom 500 to 10⁴ and a softening point <100° C., corresponding to thefollowing general formula:

    R--(X).sub.n

wherein R represents a n-valent (poly)ether residue or (poly)esterresidue having an average molecular weight of from 500 to 10,000; nrepresents an integer from 1 to 4; and X represents one of the followinggroups X₁ to X₇ when R represents a polyether residue; X₁ is--Q--O--CO--CR¹ ═CH₂ wherein R¹ represents H or CH₃ and Q is a singlebond, a polyepoxide moiety or a polyurethane moiety; X₂ is --NR² Hwherein R² represents H or C₁₋₁₈ alkyl; X₃ is --O--CO--O--R³ wherein R³represents C₁₋₁₈ alkyl or substituted or unsubstituted aryl having fromC₆ -C₁₉ ; X₄ is --O--CO--CO--O--R³ wherein R³ is as defined in X₃ ; X₅is ##STR6## wherein m is 4-11; X₆ is ##STR7## wherein A represents abond or ##STR8## wherein Z represents a (cyclo)aliphatic C₁₋₁₀ group, anaromatic C₆₋₁₆ group or an aliphatic-aromatic C₇₋₁₈ group; and X₇ is##STR9## and when R represents a (poly)ester residue, X represents oneof the following groups: X₁, X₃, X₄ or X₆, with the proviso that X₁ isnot a polyurethane moiety.
 2. Compositions as claimed in claim 1comprising from 2 to 6%, by weight, of at least one end group-modifiedpolyether and/or polyester.
 3. Compositions as claimed in claim 1comprising at least one end group-modified polyether and/or polyesterhaving a molecular weight of from 1000 to
 5000. 4. Compositions asclaimed in claim 1, wherein the polyether has --O--CO--CR¹ ═CH₂ or --NR²H end groups and the polyester has X₁ or X₆ end groups.
 5. Compositionsas claimed in claim 4 wherein a polyether with (meth)acrylate or primaryamino end groups is used.
 6. Compositions as claimed in claim 1, whereinthe polyamide is an aliphatic polyamide.
 7. Compositions as claimed inclaim 6, wherein the polyamide is polyamide-6 or polyamide-6,6optionally blended with up to 30% by weight of an elastomeric polymer.